Wing Mold

Wing Mold
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Wing Mold - 7/1/2004 5:28:50 PM

daven

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I'm hoping to be laying up some wings in a mold in the next couple of months and had some questions.

1. What are the advantages/disadvantages of using Rohacell vs. Balsa as the sandwich material for the wing?

2. Any good sources for Rohacell? I found one called Mr. Fiberglast and that looked pretty good, just curious if there were others.

3. I plan on laying up each half of the mold, and then bagging until dry. Clean up the edges, add the internal structure, and then join the two halves. This is the only way I can see keeping them light enough for my use. My question here, is that when I lay up each half, I assume that some glass will extend past the top of the mold. When I apply vacumm, where will this excess go, and how would I clean it up after it dries?

4. After the two halves are done, and I'm getting ready to put it all together, what mixture are you guys using. I assume some slow cure epoxy mixed with Cabosil?? Just curious as to the consistancy, or if I should be using somthing else.

If it matters, the wing will be 52" long with a 9 5/8" chord. The wing will hit speeds around 170 mph so strength is obviously an issue.

The wings will need to come in between 15-17 ounces at most.

This is all new to me, so I will kinda be learning as I go. I figure the first couple of wings will probably be on the heavy side, but the project will be worthless if I can't get them down to 16 ounces. There are several guys getting them there, so I know if can be done. I will be talking to them, but thought the experts here could help me start to get some info.

Thanks in advance.

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RE: Wing Mold - 7/1/2004 10:00:38 PM

sayno2glo

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From: helsinki, FINLAND
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Mother of all molding threads:
http://www.rcgroups.com/forums/showthread.php?s=&threadid=141255&perpage=15&highlight=Eisvogel&pagenumber=10

I would go for contest grade balsa because it's easier to work with more robust and gives more strength. Make sure you have enough carbon in the spar and I would recommend to ask someone who has already built similar wings. End grain balsa is good for shear web. I talk about spar this much because without good one it's will snap.
Back to Rohacell- I would use it only if I could not build light enough from balsa. When a Rohacell gets hit it will brake much more than balsa, the difference is huge.
For joining halves I use mix of epoxy, micro-balloons, carbosil, little bit of chopped class or cotton, and sometimes foaming agent (not for joining spar caps to shear web) which will make about 50% foaming when curing, but it makes the mix much weaker.

/Antti

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RE: Wing Mold - 7/1/2004 10:04:13 PM

davidfee

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From: San Diego, CA, USA
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Dave,
Here are some basic answers:

1) Rohacell is lighter than most balsa you will find. It can also have better compressive strength. Not better than end-grain balsa, but better than across a normal sheet.

2) Composite Structures Technology (CST) sells it. There are probably dozens of sources.

3) Yep, that's how it goes. Any excess material (you can cut the skins to ~exact size using templates) will be pressed flat on the mold flanges. You can trim it after curing with a sharp razor blade or chisel.

4) Epoxy and microballoons... lots of microballoons. Apply a thin bead around the perimeter and all spars/ribs using a large syringe.

Good luck,
-David

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RE: Wing Mold - 7/1/2004 10:08:57 PM

davidfee

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Antti,
That wing mold looks great! That's a new one, right? Not your Avionik clone...

Balsa is also cheaper than Rohacell... another advantage.

-David

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RE: Wing Mold - 7/1/2004 10:25:02 PM

sayno2glo

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...Avionik Killer...

There it is, intentionally fuzzy picture of it

/Antti

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RE: Wing Mold - 7/1/2004 10:37:45 PM

davidfee

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Awesome! I can't wait to see it in York!!

-David

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RE: Wing Mold - 7/1/2004 11:18:20 PM

Marco Vergara

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From: Mexico D.F., MEXICO
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Hi Dave

1.- Rohacell dents more easily and the price is higher than contest balsa wood. I use contest balsa on my wing skins q500 or q40 type.
3.- Trim the excess after the resin cure.
4.- Mix cabosil, lots of microballoms and resin. consistency should be like peanut butter.

To get a light wing you must be very careful with excess resin, select your wood, use peel ply on the entire skin surface for mold closing use very very little mixed resin.

To hold high G forces I use 3 plys of 3/4 " x 48" long carbon uni graphite stitched 4.5 oz upper and lower skin. The spar is 3/8 " cross grained balsa.

hope it helps

Marco

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RE: Wing Mold - 7/2/2004 3:15:10 AM

daven

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Antti,

Thanks for the link, that is very helpful. I will be very carefull with the spar, I was planning on 1/4" end grain balsa capped with .007 carbon fiber?? I'm suprised you mentioned balsa being easier to work with. I figured I could buy a 24" x 48" piece of rohacell and just cut it out with a razor blade. With Balsa, I'd have to go to the trouble of edge glueing the sheets and sanding. From what I saw, the Rohacell would be more money, but I found the 24" x 48" sheet of rohacell for about $40 U.S. Dollars which didn't seem to bad to me. As to durability, when these planes crash there typically isn't much left worth repairing anyways. You mentioned a foaming agent, what is this?

David,

Do you not use cabosil with your mixture to join the halves? My biggest worry is that the leading edge will open up, and the wing will explode.

Marco,

This mold will be for a ama 428 Q500 wing, so you understand what I'm doing. Your pictures were great, and I am sure I will be contacting you with questions in the future. What thickness of carbon are you using around the wing hold down bolts?

Thanks again, you've all been very helpfull.

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RE: Wing Mold - 7/2/2004 3:31:59 AM

Goggles

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#2 - I've been looking into ALL kinds of sandwich material to keep my stuff light and I'll be trying a few different materials soon to see what I can come up with. I'll let you know.

#3 - What I have found is when it's still a little tacky (green) is the best time to trim the edge. When it's dry it very hard and when it's green it a little easier to cut.

#4 - Contact East, check out their list of adhesives.....Very strong. I seen a few all composite planes that were joined with some of this stuff and talk about strong!! I have started using it and with a 3000-5000 shear strength I'm sure my stuff won't fall apart.

Take a close look at the picture, you'll see the adhesive used. (no, it's not mine)

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< Message edited by Goggles -- 7/1/2004 10:40:21 PM >

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RE: Wing Mold - 7/2/2004 3:54:58 AM

daven

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Wow Goggles, you sure that thing has enough aileron throw

That is one beautifull looking structure.

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RE: Wing Mold - 7/2/2004 4:02:33 AM

Goggles

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No kidding, but like I said it isn't mine, it's JohnVH's new kit. I seen it in person and it's HUGE!! The new CA Yak 3.3M, all composite and I took a really close look at how it was made.....amazing is all I can say. Very interesting how it's all put together, the sandwich material used, and whole structure is something to behold.

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RE: Wing Mold - 7/2/2004 4:08:50 AM

Marco Vergara

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Daven,
It is the same that I use for the spar Uni-graphite stitched 4.5 oz , I buy it at Aerospace Composite Products (ACP) if you have more questions just ask it will be a pleasure to help.

Marco

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RE: Wing Mold - 7/2/2004 9:51:49 AM

davidfee

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Dave,
No, I have not used cabosil in the joining mixture. My efforts have focused on keeping things light.

If you are trying to make it strong, then you should use some chopped glass or something. Cabosil won't really add any strength. It's just a thixotropic agent which keeps the mix from flowing down into the wing.

-David

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RE: Wing Mold - 7/2/2004 12:12:40 PM

sayno2glo

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From: helsinki, FINLAND
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quote:

ORIGINAL: daven
Antti,
Thanks for the link, that is very helpful. I will be very carefull with the spar, I was planning on 1/4" end grain balsa capped with .007 carbon fiber?? I'm suprised you mentioned balsa being easier to work with. I figured I could buy a 24" x 48" piece of rohacell and just cut it out with a razor blade. With Balsa, I'd have to go to the trouble of edge glueing the sheets and sanding. From what I saw, the Rohacell would be more money, but I found the 24" x 48" sheet of rohacell for about $40 U.S. Dollars which didn't seem to bad to me. As to durability, when these planes crash there typically isn't much left worth repairing anyways. You mentioned a foaming agent, what is this?

I assumed you are building Q40